1. Field of the Invention
This invention relates to a novel heterofunctional composition useful in immobilizing reagents on plastic surfaces. More specifically this invention comprises a molecule with hydrophobic regions that can intercalate into plastic and a hydrophilic reactive group that can covalently attach to other molecules.
2. Background Information
The practice of biotechnology, and particularly diagnostics, has increased the demand for products requiring immobilized reagents. "Reagents" includes proteins, nucleic acids, cells, drugs, and small molecule haptens. Substrates are insoluble matrices for immobilization and can be plastic, glass, silica, carbon, cellulose, or other materials. Plastics are particularly useful substrates as they can be formed into a variety of shapes, such as cups, discs, "dipsticks", spheres, tubes, membranes, and particles. Additionally, plastics have a high degree of biocompatability, and may be produced of materials having excellent optical properties. Typical plastics useful as substrates include polypropylene, polystyrene, polyethylene, polyvinyl chloride, polysulfone, polycarbonate, cellulose acetate, and others. Polystyrene, polyvinyl chloride, and polycarbonate are widely used substrates when optical properties are a consideration. Plastics themselves are often used as substrates for direct immobilization of macromolecules. Polystyrene and polyvinyl chloride will anchor large molecules by electrostatic attraction. However, small molecules require attachment to larger "carrier" molecules to be bound. Also, poor absorption to most plastics limit the use of absorption immobilization to high surface area systems. For instance, polystyrene latex particles can immobilize protein molecules although molded polystyrene products usually require plastic modifying agents due to the limited surface area.
Modification of the plastic surface has been used to increase the electrostatic interaction and increase the binding of some reagents. Electrostatic interactions alone will immobilize only a limited number of reagents, and when detergents are introduced in the system reagent loss can occur.
Reagent molecules are typically immobilized on a substrate by way of a linker molecule. Homofunctional and heterofunctional compounds have been devised to link a group present on the reagent to a group present on the substrate. As an example, disuccimidyl suberate is a homofunctional compound that can covalently bridge an amine group on a reagent molecule to an amine group present on a substrate, such as aminopolystyrene. Additionally, some plastics, such as methyl methacrylate and polyethylvinylacetate, have been developed to bear hydroxyls that can be converted to reactive intermediates. Reactive groups that can be provided include epoxides, hydroxy succinimide esters, aldehydes, nitrophenyl chloroformate, activated thiols, trityl, tresyl chloride, or other means for reacting free amines, hydroxides or sulfhydryls.
Modification of the plastic surfaces to bear amines, hydroxyls, and sulfhydryls that can be crosslinked or otherwise modified has resulted in undesirable characteristics, particularly opacity.
One system that has become available involves incorporation of a methyl imine function. This product requires the end user to convert the methyl imine functionality to a reactive group by addition of crosslinkers (NUNC, Naperville, Ill.). Another system treats plastic with a copolymer of phenylalanine and lysine amino acids to provide a support for a crosslinker (U.S. Pat. No. 4,657,873; Gadaro, 1987).
Thus, a need continues to exist for a heterofunctional product that can directly modify a plastic surface to provide a covalent coupling means.